# Java easy understand code DP

• ``````public int coinChange(int[] coins, int amount) {
if (coins == null || coins.length == 0 || amount < 0) {
return -1;
}
int[] f = new int[amount + 1];
f[0] = 0;
for (int coin : coins) {
if (coin > amount) {
break;
}
f[coin] = 1;
}
for (int i = 1; i <= amount; i++) {
if (f[i] == 0) {
f[i] = Integer.MAX_VALUE;
}
}
for (int i = 1; i <= amount; i++) {
for (int j = 0; j < coins.length; j++) {
if (coins[j] <= i && f[i - coins[j]] != Integer.MAX_VALUE) {
f[i] = Math.min(f[i], 1 + f[i - coins[j]]);
}
}
}
return f[amount] == Integer.MAX_VALUE ? -1 : f[amount];
}``````

• Do we need "if (f[i] == 0)" in "for (int i = 1; i <= amount; i++)"?
looks like the "f" array only has 0 in index 0 but "i" starts from 1.

• for (int coin : coins) {
if (coin > amount) {
break;
}
f[coin] = 1;
}

This part, so if we use int coin : coins, the coin will be in increasing order automatically? Otherwise, if the coins is [230, 250, 3] and amount is 233, then we break at coin = 250 and f[3] is never set to be 1.

• hey, think of this, when you init an array, what is the initial value for all the array members?

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